@CB
Thanks for the tips. I will have to try those on my next try.
As far as an update on the general lock screen ad campaign.
It's been a long time since I've done it (so long that all my 'associate sales' sites no longer work), but I once had access to a site where you'd post one story, and the book would draw links to every other story linked to yours, based on readers who purchased them.
Thus, you'd either list a book somewhat like yours, or list your own book, observe what your readers also purchased (or at least visited after viewing your books, and then used those to target your adds. After all, there's no sense linking your book to a story that only one fan read, but one that a majority of your readers liked, that's also selling millions of copies, that's one that's worth sinking some bucks into.
However, the easiest way to do this is with Amazon keyword searches. Simply search for books based on each keyword you select, and it'll list how often the keywords are used, as there's little sense if promoting SEO keywords that no one will ever type in a global search. Then, once you have the list of optimal keywords, simply type them all in a identify the top 20 books which match those same keywords, filtered by your specific genre.
But with sites increasingly cracking down of online marketing, the older tools are often no longer available to directly track which books are most directly related to yours, so now it's once again mostly a crap shoot!
But the key terms are "Sponsored ads", tied to other, more successful books that are similar to yours, and "Lockscreen ads", which are more typically tied to specific SEO keywords (ex: "lesbian goth mysteries", "steampunk" or "disgraced ex cop").
Lockscreen ads in particular are good, as they'll specifically list books with the tagline "Like so and so author? You'll love this." Unfortunately, Lockscreen ads ONLY appear when someones actually enters a site and then searches by keyword, which not a lot of authors bother to do.